This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Nuclear sclerotic cataract is associated with oxidative damage to the lens proteins. Exposure of the lens to increased oxygen and loss of the gel structure of the vitreous body lead to nuclear cataract formation. Based on the distribution of oxygen in human eyes, we hypothesized that the vitreous activity consumes oxygen, which minimizes oxygen exposure to the lens. Vitreous oxygen consumption was measured using a microrespirometer fitted to an optical oxygen sensor. Vitreous ascorbate was measured spectrophotometrically and confirmed by gas chromatography/mass spectrometry. The gel state of the vitreous was assessed and related ot the rate of oxygen consumption and ascorbate concentration in samples obtained postmortem andd at the beginning of vitrectomy surgery.